The present invention relates generally to fluid pumps, and more particularly to deforming a viscoelastic material to propel fluid through the pump, an ink jet print head utilizing the pump, and a method of pumping fluid.
Various types of pumps are known for use in xe2x80x9cdrop on demandxe2x80x9d (DOD) print heads, such as ink jet print heads. For example, in a thermal type bubble jet printer, ink in a channel is heated to a boil to create a bubble until the pressure ejects a droplet of the ink out of a nozzle. The bubble then collapses as the heating element cools, and the resulting vacuum draws fluid from a reservoir to replace the fluid that was ejected from the channel. Such thermal types of pumps require that the ink be resistant to heat, i.e. capable of being boiled without significant breakdown. Also, the need for a cooling period between ejecting successive droplets from a nozzle places speed limitations on thermal pumps.
Piezoelectric pumps, such as that disclosed in U.S. Pat. No. 5,224,843, have a piezoelectric crystal in the fluid channel that flexes when an electric current flows through it to force a drop of fluid out of a nozzle. Piezoelectric technology provides more control over the fluid movement as compared to thermal technology. Also, because the fluid to be pumped is not heated significantly, the fluid can be selected based on its relevant properties rather than its ability to withstand high temperatures. However, piezoelectric microscale pumps are complex and thus expensive to manufacture. For example, piezoelectric materials generally are not suitable for interface with fluids and thus inner walls of the ink chamber must be coated with metal or the like. Further, piezoelectric devices generally are not compatible with known CMOS processes. Also, ink chambers incorporating piezoelectric materials are difficult to form, usually requiring that the piezoelectric material be sawed and glued. Finally, Piezoelectric pumps require a relatively large voltage for adequate wall deflection for most print head applications, e.g. 30-35 volts for a 2 nm deflection.
It is also known to place a modulated electric field across an elastomer to deform the elastomer in conformance with an image and to read out the image from the deformed elastomer. This device is known as the xe2x80x9cRuticonxe2x80x9d device and is disclosed, for example, in U.S. Pat. No. 3,716,359.
An object of the invention is to decrease the voltage required for pumping ink in DOD print heads.
Another object of the invention is to simplify the construction of DOD print heads.
Another object of the invention is to utilize semiconductor fabrication techniques to manufacture a fluid pump.
Another object of the invention is to utilize standard CMOS processes to manufacture a fluid pump.
Another object of the invention is to reduce costs associated with manufacturing DOD print heads.
The invention achieves these and other objects through a first aspect of the invention which is a print head comprising an ink channel having a nozzle and at least one wall having a flexible portion, a deforming member coupled to the flexible portion, and a charging mechanism coupled to the deforming member and configured to apply a spatially varied charge pattern to the deforming member when the charge mechanism is activated. Activation of the charge mechanism causes deformation of the deforming member and the flexible member to thereby reduce the volume of the ink channel and eject a droplet of ink out of the ink channel.
A second aspect of the invention is a fluid pump comprising a fluid channel having a nozzle and at least one wall having a flexible portion, a deforming member coupled to the flexible portion, and a charge mechanism coupled to the deforming member and configured to apply a spatially varied charge pattern to the deforming member when the charge mechanism is activated. Activation of the charge mechanism causes deformation of the deforming member and the flexible member to thereby reduce the volume of the fluid channel and eject fluid out of the fluid channel.
A third aspect of the invention is a method of pumping a fluid comprising the steps of coupling a deforming member to a flexible portion of a fluid channel, and reducing the volume of the fluid channel by applying a spatially varied charge pattern to the deforming member to cause deformation of the deforming member and the flexible member to eject fluid out of the fluid channel.